Recent electronic components are generally driven by low voltage to reduce power consumption. A DC-DC converter is used to generate power-supply voltage for such an electronic circuit.
In the DC-DC converter, the amount of current which can flow through a load is determined in advance. When the current exceeding the predetermined level passes through the load, power-supply voltage level is lowered and desired electrical characteristics cannot be obtained.
In the development stage of an electronic circuit, it is difficult to correctly estimate the total capacity of loads. Normally, a certain level of margin is set for load capacity and a DC-DC converter corresponding thereto is employed. However, there is a case where load capacity slightly exceeds the level previously estimated, in the final development stage of the electronic circuit. In such a case, it is generally difficult to secure sufficient time for replacing the DC-DC converter by a high-current type. Accordingly, as a countermeasure for this problem, the number of DC-DC converters to be employed is increased by one or more to increase current capacity.
When a plurality of DC-DC converters are connected in parallel to a power-supply line, it is ideal that each DC-DC converter operates evenly. However, in actual cases, some DC-DC converters may operate unevenly due to the variation in electronic components in the DC-DC converter. Accordingly, current supply to a large capacity load cannot be shared by a plurality of DC-DC converters, which leads to a problem that the power-supply voltage of the electronic circuit on the load side is reduced.